Inert gas

Inert gas

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An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration. Neon
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...

 and argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

 are the most common inert gases for use in chemistry and archival settings.

Unlike noble gas
Noble gas
The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity...

es, an inert gas is not necessarily elemental and is often a compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 gas. Like the noble gases the tendency for non-reactivity is due to the valence, the outermost electron shell
Electron shell
An electron shell may be thought of as an orbit followed by electrons around an atom's nucleus. The closest shell to the nucleus is called the "1 shell" , followed by the "2 shell" , then the "3 shell" , and so on further and further from the nucleus. The shell letters K,L,M,.....

, being complete in all the inert gases. This is a tendency, not a rule, as noble gases and other "inert" gases can react to form compounds.

In marine applications, the term "inert gas" is used for gases with a low content of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 that are used to fill void spaces in and around tanks for explosion protection
Explosion protection
Explosion protection is used to protect all sorts of buildings and civil engineering infrastructure against internal and external explosions or deflagrations. It was widely believed until recently that a building subject to an explosive attack had a chance to remain standing only if it possessed...

. There are two types of inert gas which are either based on nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 or on flue gas
Flue gas
Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. Quite often, the flue gas refers to the combustion exhaust gas produced at power plants...

.

In underwater diving
Underwater diving
Underwater diving is the practice of going underwater, either with breathing apparatus or by breath-holding .Recreational diving is a popular activity...

 an inert gas is a component of the breathing mixture which is not metabolically active, and serves to dilute the gas mixture. The inert gas may have effects on the diver, but these are thought to be mostly physical effects, such as tissue damage caused by bubbles in decompression sickness. The most common inert gases used in breathing gases for diving are nitrogen and helium.

Production


The elemental inert gases are usually obtained by evaporating them off from condensed air at their respective vapor pressure
Vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...

s.

Nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

-based inert gases are produced on board chemical tankers and product carrieres (smaller vessels) with compressors and a nitrogen-specific membrane.

Inert gas is produced on board crude oil carriers (above 20000 tonnes) by using either a Flue Gas system or by burning kerosene in a dedicated inert gas generator
Inert gas generator
Inert gas generator refers to machinery on board marine product tankers. Inert gas generators consist distinctively of a burning and cooling chamber.Atmospheric air is burned so that it contains less than 5% oxygen, thereby creating "inert gas"...

. The flue gas system uses the boiler exhaust as its source, so it's important that the fuel/air ratio in the boiler burners is properly regulated to ensure that high quality IG is produced. Too much air would result in an oxygen content exceeding 5%, too much fuel oil would result in carryover of dangerous hydrocarbon gas. The flue gas is cleaned and cooled by the scrubber tower. Various safety devices prevent overpressure, return of hydrocarbon gas to the engine room or supply of IG with too high oxygen content.

Gas tankers and product carriers cannot rely on flue gas systems (because they require IG with O2 content of 1% or less) and so use IGGs instead. The Inert Gas Generator consists of a combustion chamber and scrubber unit supplied by fans and a refrigeration unit which cools the gas. A drier in series with the system removes moisture from the gas before it is supplied to the deck.

Regular calibration and testing to equipment is required to ensure that it works correctly.

Applications


Because of the non-reactive properties of inert gases they are often useful to prevent undesirable chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...

s from taking place. For example molecular nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

, a molecular inert gas, is often used in food packaging to ensure that food does not spoil in transit since no bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 or fungi can flourish without the reactive gases oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 or carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, which the molecular nitrogen displaces, since most extant cells on Earth require the reactions which these gases are involved in to function. Most importantly since molecular nitrogen is inert it will not cause any reactions to take place in the food, possibly changing the intrinsic taste or smell, nor will it cause any chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...

s in the human body
Human body
The human body is the entire structure of a human organism, and consists of a head, neck, torso, two arms and two legs.By the time the human reaches adulthood, the body consists of close to 100 trillion cells, the basic unit of life...

. Thus the inert gas is used as a passive preservative, preventing biological decay, while being undetectable to the consumer since taste and olfactory senses require a chemical reaction to take place in order to send a signal to the brain. This is in contrast to active preservatives which react with the biological material of bacteria, fungi, and possibly the food itself changing the food's intrinsic taste or smell, or may even act directly on the consumer's taste and olfactory mechanisms.

As chemists sometimes need to perform experiments on air-sensitive compounds, air-free technique
Air-free technique
Air-free techniques refer to a range of manipulations in the chemistry laboratory for the handling of compounds that are air-sensitive. These techniques prevent the compounds from reacting with components of air, usually water and oxygen; less commonly carbon dioxide and nitrogen...

s have been developed to handle them under inert gas.

Several Noble gas
Noble gas
The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity...

es are commonly used inside gas-discharge lamp
Gas-discharge lamp
Gas-discharge lamps are a family of artificial light sources that generate light by sending an electrical discharge through an ionized gas, i.e. a plasma. The character of the gas discharge critically depends on the frequency or modulation of the current: see the entry on a frequency classification...

s, such as "neon lights
Neon lighting
Neon lighting is created by brightly glowing, electrified glass tubes or bulbs that contain rarefied neon or other gases. Georges Claude, a French engineer and inventor, presented neon tube lighting in essentially its modern form at the Paris Motor Show from December 3–18, 1910...

". In neon sign
Neon sign
Neon signs are made using electrified, luminous tube lights that contain rarefied neon or other gases. They are the most common use for neon lighting, which was first demonstrated in a modern form in December, 1910 by Georges Claude at the Paris Motor Show. While they are used worldwide, neon signs...

s they are used to produce different colors. They are also used in excimer laser
Excimer laser
An excimer laser is a form of ultraviolet laser which is commonly used in the production of microelectronic devices , eye surgery, and micromachining....

s.

Welding


In Gas Tungsten Arc Welding (GTAW) inert gases are used to shield the tungsten from contamination. It also shields the fluid metal (created from the arc) from the reactive gases in air which can cause porosity in the solidified weld puddle. Inert gases are also used in Gas Metal Arc Welding (GMAW) for welding non-ferrous metals. Some gases which are not usually considered inert but which behave like inert gases in all the circumstances likely to be encountered in some use can often be used as a substitute for an inert gas. This is useful when an appropriate pseudo-inert gas can be found which is inexpensive and common. For example, carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 is sometimes used in gas mixtures for GMAW because it is not reactive to the weld pool created by arc welding. But it is reactive to the arc. The more carbon dioxide that is added to the inert gas, such as argon, will increase your penetration. The amount of carbon dioxide is often determined by what kind of transfer you will be using in GMAW. The most common is Spray Arc Transfer, and the most commonly used gas mixture for spray arc transfer is 85% argon and 15% carbon dioxide. (Listed as many different names depending on the gas supplier).

Inert gas blanketing


On oil tankers inert gas (IG) is used to prevent the atmosphere in cargo tank
Tank
A tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility, tactical offensive, and defensive capabilities...

s or bunker
Bunker
A military bunker is a hardened shelter, often buried partly or fully underground, designed to protect the inhabitants from falling bombs or other attacks...

s from coming into the explosive range. IG keeps the oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 content of the tank atmosphere below 8% (on crude carriers, less for product carriers and gas tankers), thus making any air/hydrocarbon gas mixture in the tank too lean to ignite. IG is most important during discharging and during the ballast voyage when more hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

 vapour is likely to be present in the tank atmosphere. IG can also be used to purge the tank of the volatile atmosphere in preparation for gas freeing - replacing the atmosphere with breathable air - or vice versa.

Cargo tanks on gas carriers are not inerted, but the hold space around them is. This arrangement allows the tanks to be kept cool using a small heel of cargo while the vessel is in ballast while retaining the explosion protection provided by the inert gas.

List of Inert Gases

  • Helium
    Helium
    Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

     (He)
  • Neon
    Neon
    Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...

     (Ne)
  • Argon
    Argon
    Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

     (Ar)
  • Krypton
    Krypton
    Krypton is a chemical element with the symbol Kr and atomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other...

     (Kr)
  • Xenon
    Xenon
    Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...

     (Xe)
  • Radon
    Radon
    Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of uranium or thorium. Its most stable isotope, 222Rn, has a half-life of 3.8 days...

     (Rn)
  • Sulfur hexafluoride
    Sulfur hexafluoride
    Sulfur hexafluoride is an inorganic, colorless, odorless, and non-flammable greenhouse gas. has an octahedral geometry, consisting of six fluorine atoms attached to a central sulfur atom. It is a hypervalent molecule. Typical for a nonpolar gas, it is poorly soluble in water but soluble in...

     (SF6)
  • Nitrogen
    Nitrogen
    Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

    (N2)